In a rotary drilling rig to be used for oil-well drilling, a bit (blade) is mounted on the forward end of a drilling pipe, and it is rotated at a high speed for drilling. The drilling portion is exposed to a high temperature, high pressure and acidic atmosphere, and therefore, a drilling member is required to have heat resistance, acid resistance and high strength.
Therefore, fluoro-rubber is used for a rubber member for oil-well drilling, such as a sealing material at a joint portion of an oil-well drilling pipe. Particularly, a tetrafluoroethylene/propylene copolymer is preferably used as a rubber material excellent in heat resistance, acid resistance and oil resistance.
However, along with the progress in drilling technology, abrasion resistance higher than ever has also been required. Therefore, a highly hard fluoro-rubber has now been required as a material for a rubber member for oil-well drilling.
Patent Document 1 discloses a method wherein a rubber composition comprising raw material rubber made of a tetrafluoroethylene/propylene copolymer and silica having its surface hydrophobized, is molded, followed by irradiation with γ-rays to produce a fluoro-rubber molded product. In Examples, as the fluoro-rubber, a tetrafluoroethylene/propylene copolymer, and as the hydrophobized silica, AEROSIL R202, manufactured by Nippon Aerosil Co., Ltd., are used.
Patent Document 2 discloses a hose made of a laminate of a fluoro-rubber layer and an acrylic rubber layer. The fluoro-rubber layer is formed by a method wherein a fluoro-rubber composition comprising fluoro-rubber, carbon black, a silica-type filler, an organic peroxide and a cross-linking assistant, is molded, followed by steam vulcanization and hot air vulcanization. In Examples, as the fluoro-rubber, a tetrafluoroethylene/propylene binary copolymer, and as the silica-type filler, AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd., are used.